Express your answer as a mixed number simplified to lowest terms. $20\dfrac{1}{8}-4\dfrac{1}{4} = {?}$
Explanation: Find a common denominator for the fractions: $= {20\dfrac{1}{8}}-{4\dfrac{2}{8}}$ Convert ${20\dfrac{1}{8}}$ to ${19 + \dfrac{8}{8} + \dfrac{1}{8}}$ So the problem becomes: ${19\dfrac{9}{8}}-{4\dfrac{2}{8}}$ Separate the whole numbers from the fractional parts: $= {19} + {\dfrac{9}{8}} - {4} - {\dfrac{2}{8}}$ Bring the whole numbers together and the fractions together: $= {19} - {4} + {\dfrac{9}{8}} - {\dfrac{2}{8}}$ Subtract the whole numbers: $=15 + {\dfrac{9}{8}} - {\dfrac{2}{8}}$ Subtract the fractions: $= 15+\dfrac{7}{8}$ Combine the whole and fractional parts into a mixed number: $= 15\dfrac{7}{8}$